Depending on your workout, a different combination of these fuel sources is used.

During intense exercises, such as weightlifting or sprinting, your muscles use glucose. First, sugar from your blood is used up, then your body breaks down the stored glycogen, which provides your body with enough sugar to keep you active for about an hour. Glucose gives your body energy fastest of any fuel, so it us used during an intense workout that requires a lot of energy quickly.

A less intense workout (one that gets your moving but doesn’t cause you to breathe heavily) uses stored body fat. Using fat to fuel your muscles requires oxygen, so whenever you start gasping for breath, you know you’re not using fat as fuel anymore, but are using glucose instead.

So… When & What Should I Eat?

Before Your Workout

If you’re not hungry, there’s no need to eat before a workout. Your body has the energy to keep you active for about an hour.

If you are hungry, eat a 100-200 calorie snack that has a combination of simple sugars and fiber and/or protein. The simple sugars will give you immediate energy, and the fiber and protein will break down more slowly, giving you sustained energy. A piece of fruit, a granola bar, small bowl of cereal, or some yogurt will work well here.

During Your Workout

If your workout is less than 90 minutesYou don’t need to eat anything during this workout. Your body’s preferred fuel, glucose, will keep you going for a while.

If your intense workout is more than 90 minutesWhen you work out intensely and burning glucose for more than 90 minutes, your glucose storage will get low, so it becomes important to refuel yourself so you don’t “hit the wall“. A small snack that’s packed with simple sugars & is easy to digest, like a handful of dried fruit or a banana, will keep you energized during a lengthy intense workout. Energy bars or gels will generally do the trick, too. Aim to consume about 100-200 calories for every additional hour of your intense workout.

Sports drinks can be an easy way to refuel during a long workout because they also hydrate and replenish electrolytes lost during exercise. Dilute your sports drinks with water to get the proper number of calories per hour– they’re often much more concentrated than your body really needs.

After Your Workout

If your workout is less than 90 minutes

Unless you are hungry, you don’t really need to eat after this workout. If you are hungry, aim for a good combination of simple sugars to replenish the glycogen stored in your muscles and protein to help rebuild your muscles. Chocolate milk, Greek yogurt, fruit with peanut butter, or a granola bar all pack in balanced mix of sugars and protein, making them good post workout snacks.

If your workout is more than 90 minutes

You’ve put your muscles through a lot in this workout and need to refuel them. Aim to eat soon after these more intense workouts (less than 2 hours) to refill your muscles’ stored glycogen and also give them the protein necessary to rebuild themselves. Aim for a combination of complex carbohydrates & protein. Some ideas for post long-workout meals include a peanut butter & jelly sandwich, oatmeal made with milk, whole-grain pasta with chicken, or any other complex carbohydrate and protein focused meal.

Generally, go by your own hunger to decide whether or not you need to eat before or after a workout. If you’re not hungry, you don’t need to eat. It’s when your workouts get longer and more intense that you really need to be sure to be replenishing your glycogen stores

So remember: if you’re hungry pre-workout, go for something like an apple, which has both simple sugars & fiber, to give you immediate and sustaining energy. After a workout, you want more complex carbohydrates and protein, which will replenish your fuel sources and rebuild your muscles. Keep that in mind, and exercise nutrition can become much more simple!